B. Leal-Acevedo, P.G. Reyes-Romero, F. Castillo and I. Gamboadebuen
Specific energy; Linear energy, PENELOPE code
|PUBLISHED DATE||August 6, 2018|
|PUBLISHER||The Author(s) 2018. This article is published with open access at www.chitkara.edu.in/publications.|
The specific and linear energy was calculated in target sizes of 10 μm, 5 μm, 1 μm, 60 nm, 40nm and 20 nm by taking into account the contribution of the primary photon beams and the electrons generated by them in LiF: Mg, Ti (TLD-100). The simulations were carried out by the code PENELOPE 2011. Using different histories of primary particles, for each energy beams the mean deposited energy is the same, but to achieve a statistical deviation lower than 1% the value of 108 was fixed. We find that setting the values C1 = 0.1 C2 = 0.1 and Wcc = Wcr = 50 eV the time of simulation decreases around the 25%. The uncertainties (1 SD) in the specific energy increases with energy for all target sizes and decreases with target size, with values from 1.7 to 94% for 20 nm and between 0.1 and 0.8% for 10 μm. As expected, the specific and linear energies decrease with target size but not in a geometrical behavior.
In the 70s Kellerer and Rossi [1, 2, 3] laid the groundwork for the ICRU to include as base quantities, the specific energy (z)and linear energy (y) to be used in microscopic structures size, these quantities correspond to dose and LET in the macroscopic world. The importance of these magnitudes is useful in the fields where the size of the structures requires the determination of the energy deposited in nanometer volumes. For the physical systems some authors [4, 5] calculated the specific energy and lineal energy where the objective is to obtain the frequency distribution for several sources and spherical water targets. In the last two decades it has been studied with special interest the capabilities of several programs using the Monte Carlo code, evaluating the position of a single interaction and the energy deposited by the secondary electrons with a lower energy threshold, regardless of the primary particle beam targets with micrometer or smaller sizes. This has been done by using simulations called event-by-event, where the coordinates of energy transfer and the energy deposited in the event are obtained [6, 7, 8]. Olko et al.  used electron transport in water vapor of unit density to determine the mean linear energy and the relative TL efficiency for LiF:Mg,Cu,P with a target sized of 60 nm and for Al2O3:C with target sized of 170 nm. The aim of this work is to investigate the interaction of monoenergetic low energy photons in the TLD-100 chip using the PENELOPE code, considering the geometry used in experiments performed to determine the relative TL response and efficiency of TLD-100 for photons beams, for different sizes of the target volume.
|ISSN||Print : 2321-8649, Online : 2321-9289|
The specific and linear energies, obtained for both the primary photons and secondary electrons at the same time, are in good agreement with those reported for spherical water targets . As expected, the specific and linear energies decrease with target size but not in a geometrical behavior. This can be due to the effect of the secondary electrons that leave the target without depositing energy in the smallest targets. It is recommended to analyze by means of the space-phase file the contribution of second generation particles to understand the way of how energy is deposited in micrometric volumes.